Full-index-fitting (FIF) approach. Top panels: Mgb 5177 (left) and the TiO₂ (right) spectral features, normalized using the index pseudo-continua (blue shaded regions). In the FIF approach, every pixel within the central bandpass (gray area) is fit to measure the stellar population parameters. The black line corresponds to a model of solar metallicity [M/H] = 0, [Mg/Fe] = 0, [Ti/Fe] = 0, and Kroupa-like IMF, at a resolution of 200 km s⁻¹. The FIF approach breaks the degeneracies more efficiently than the standard line-strength analysis because every pixel responds differently to changes in the stellar population properties. Colors in the bottom panels show the relative change in the spectrum after different stellar population parameters were varied. For reference, the IMF slope was varied by ΔΓ_B = 1, the metallicity and abundance ratios by 0.2 dex, and the age by 2 Gyr.